Continuous production of solid products from reactive gases typically entails reacting the reactive gases in the presence of a catalyst in such a way that the solid products are elutriated from the surface of the catalyst. The solid products are thus swept away from the catalyst and subsequently harvested in a suitable process or series of processes for removing particulates from reaction tail-gases. Reactors conventionally used for such continuous solid production include fluidized-bed reactors, fixed bed reactors, pulsed bed reactors, shaft kilns, etc. Particulate removal devices typically include cyclones, bag houses, electrostatic precipitators, scrubbers, etc.
Various morphologies and allotropes of carbon are used industrially, such as for fuel, as reducing agents and electrodes in metallurgical processes, as corrosion-resistant materials in furnaces and heat exchangers, as carbon electrodes, as fillers and colorants in plastics, rubbers and inks, and as strengtheners in many polymer formulations including tires and hoses. High-purity carbon in many allotropes and morphologies is a bulk commodity chemical widely used in industry. Carbon nanotubes (CNTs) may be particularly valuable.
CNTs may be used for various emerging applications because of their remarkable material properties. CNT use in various manufacturing processes potentially adds strength, toughness, impact resistance, electrical conductivity, and/or thermal conductivity to a product. Currently, CNTs are one of the more expensive allotropes of carbon, and the cost, availability, and quality limit broad industrial uses of this material. Methods for producing CNTs that reduce costs and improve availability and quality would therefore be useful.
CNTs may be produced in a variety of sizes and types. Background information on carbon nanotubes is included in U.S. Patent Application Publication No. 2012/0034150 A1, titled “Method for Producing Solid Carbon by Reducing Carbon Oxides,” and published on Feb. 9, 2012, the contents of which are incorporated by this reference. There are two main classes of carbon nanotubes: single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs). CNTs are typically produced using methods that form primarily SWNTs or primarily MWNTs of various lengths and diameters. One CNT manufacturing process, described in U.S. Patent Application Publication No. 2012/0034150, may produce a mixture of both MWNTs and SWNTs.